Rechargeable lithium battery

ABSTRACT

Disclosed is a rechargeable lithium battery that includes a positive electrode including a lithium nickel-based positive active material; a negative electrode including a negative active material; an electrolyte including a lithium salt and a non-aqueous organic solvent; and a separator including a polymer substrate and a hydroxide compound-containing coating layer disposed on the polymer substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C. §120 as a Continuation of,U.S. Ser. No. 13/805,855 filed on 20 Aug. 2010. All benefits under 35U.S.C. §120 are claimed.

This application also claims priority from Korean Patent Application No.10-2009-0114810, entitled RECHARGEABLE LITHIUM BATTERY, filed 25 Nov.2009, the entire contents of which are incorporated herein by reference.All rights of priority and benefits available under 35 U.S.C. §119 areclaimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates to a rechargeable lithium battery.

2. Description of the Related Art

Lithium rechargeable batteries have recently drawn attention as a powersource for small portable electronic devices. They use an organicelectrolyte solution, and thereby have twice the discharge voltage of aconventional battery using an alkaline aqueous solution and,accordingly, high energy density. Such a rechargeable lithium batteryincludes a positive electrode, a negative electrode, and an electrolyte.

For positive active materials of a rechargeable lithium battery,composite metal oxides such as LiCoO₂, LiMn₂O₄, LiNi_(1-x)Co_(x)O₂(0<x<1), and the like have been suggested. As for negative activematerials of a rechargeable lithium battery, various carbon-basedmaterials such as artificial graphite, natural graphite, and hardcarbon, or non-carbon-based materials such as silicon, tin oxide,lithium vanadium-based oxide, and the like have been suggested. Aseparator is disposed between positive and negative electrodes forseparating the electrodes and generally, includes polymer filmsincluding insulating polymers such as polyethylene, polypropylene, andthe like.

SUMMARY OF THE INVENTION

One aspect of this disclosure provides a rechargeable lithium batteryhaving excellent cycle-life at high temperatures.

According to one aspect of this disclosure, a rechargeable lithiumbattery is provided that includes a positive electrode including apositive active material comprising lithium and nickel; a negativeelectrode including a negative active material; an electrolyte includinga lithium salt and a non-aqueous organic solvent; and a separatorincluding a polymer substrate and a coating layer comprising a hydroxidecompound disposed on the polymer substrate.

The hydroxide compound may include Al(OH)₃, Mg(OH)₂, Ti(OH)₄, Si(OH)₄,or a combination thereof.

The coating layer may further include a heat-resistant resin.

The polymer substrate may be a substrate including a polyolefin resin.

The non-aqueous organic solvent includes an ethylene carbonate organicsolvent represented by the following Chemical Formula 4, (hereinafter,referred to “ethylene carbonate-based organic solvent”), and theethylene carbonate-based organic solvent may be included in an amount ofabout 10 to 30 wt % based on the total amount of the non-aqueous organicsolvent. The ethylene carbonate-based organic solvent may includefluoroethylene carbonate.

In the above Chemical Formula 4, R₁ and R₂ are the same or different,and are hydrogen, a halogen, a cyano (CN), a nitro (NO₂), or asubstituted alkyl, provided that at least one of R₁ and R₂ is a halogenor a substituted alkyl. The alkyl may be a C1 to C5 alkyl. Thesubstituted alkyl may be an alkyl in which at least one hydrogen issubstituted with fluorine.

The negative active material includes Si, SiO_(x) (0<x<2), a Si-Q alloy,or a combination thereof. Herein, Q is an alkali metal, analkaline-earth metal, a Group 13 element, a Group 14 element, transitionelements, or a rare earth element, or a combination thereof, providedthat Q is not Si.

The positive active material may include at least one of compoundsrepresented by the following Chemical Formulae l to 3, or a combinationthereof.

Li_(g)Ni_(h)L_(1-j)O_(e)   Chemical Formula 1

In the Chemical Formula 1, 0.8≦g≦2, 0≦h≦1, e is 1 to 2, 0≦j≦1, and

L is Al, Mn, Mg, Zr, or La, or a combination thereof.

Li_(x)Ni_(y)Co_(z)L′_(1-y-z)O_(q)   Chemical Formula 2

In the Chemical Formula 2, 0.65≦x≦1, 0≦y≦1, 0≦z≦1, 0≦y+z≦1, q rangesfrom 1.8 to 2, and

L′ is Al, Mn, Mg, Zr, or La, or a combination thereof.

Li_(x)MO_(2-z)L_(z)   Chemical Formula 3

In the above Chemical Formula 3, M is M′_(1-k)A_(k) (M′ isNi_(1-d-e)Mn_(d)Co_(e), 0.65≦d+e≦0.85, 0.1≦e≦0.4, A is a dopant, and0≦k<0.05),

L is F, S, or P, or a combination thereof,

0.95≦x≦1.05, and

0≦z≦2.

The rechargeable lithium battery may be a high voltage rechargeablelithium battery having an operating voltage of about 4.35V to about4.5V.

The rechargeable lithium battery has improved room temperature and hightemperature cycle-lives.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view of a rechargeable lithium battery accordingto one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments will hereinafter be described in detail. However,these embodiments are only exemplary, and this disclosure is not limitedthereto.

The rechargeable lithium battery according to one embodiment includes apositive electrode including a lithium nickel positive active material;a negative electrode including a negative active material; anelectrolyte including a lithium salt and a non-aqueous organic solvent;and a separator.

The rechargeable lithium battery may be a high voltage rechargeablelithium battery having an operating voltage of about 4.35V to about4.5V.

The separator includes a polymer substrate and a hydroxidecompound-containing coating layer disposed on the polymer substrate. Thecoating layer may be disposed on one side of polymer substrate or bothsides of the polymer substrate.

The hydroxide compound may include Al(OH)₃, Mg(OH)₂, Ti(OH)₄, orSi(OH)₄, or a combination thereof. When this hydroxide compound isdisposed into a coating layer, it has weak particle strength,particularly weaker than an oxide like alumina, and thus, may produce aparticle less worn out while mixed. Accordingly, there may be lessimpurities, improving the process.

The coating layer may further include a heat-resistant resin as abinder. Such a heat-resistant resin includes an aramid resin, apolyamideimide resin, or a polyimide resin, or a combination thereof.

The aramid resin indicates an aromatic polyamide resin, and for example,includes a meta-aramid resin in which phenyl groups are all linked intoa backbone chain via meta-linkage except for an amide group, or apara-aramid resin in which phenyl groups are all linked into a backbonechain via para-linkage except for an amide group.

In addition, any heat-resistant resin supplying heat resistance, buthaving no bad influence, may be used.

In other words, the coating layer may be disposed by mixing a hydroxidecompound and a heat-resistant resin in a solvent and coating thecomposition on a polymer substrate. The solvent may be volatilizedduring the drying, leaving only the hydroxide compound and the aramidresin in the coating layer.

Herein, the hydroxide compound and the heat-resistant resin are mixed ina ratio ranging from 50:50 to 90:10 wt % but in another embodiment,ranging from 60:40 to 80:20 wt %. When they are mixed within the ratiorange, they may bring about appropriate pore formation, control of metalion elution, easy coating of a separator, and heat resistance.

Since the hydroxide compound and the heat-resistant resin are mixedwithin the ratio and form a coating layer, they may be left in thecoating layer within the same ratio.

In addition, the solvent may include any organic solvent that maydissolve the heat-resistant resin and for example, may includeN-methylpyrrolidone.

The polymer substrate may be a substrate including a polyolefin. Thepolyolefin includes a polyethylene-based resin, or a polypropylene-basedresin, or a combination thereof.

Specific examples may include a polyethylene-based resin such as lowdensity polyethylene, linear polyethylene (ethylene-α-olefin copolymer),high density polyethylene, and the like or a polypropylene-based resinsuch as polypropylene, ethylene-propylene copolymer, and the like.

The polymer substrate may be 8 to 20 μm thick but in another embodiment,10 to 15 μm thick. When it has a thickness within these ranges, it maybring about appropriate shut-down function effects.

The hydroxide compound-containing coating layer may be 2 to 8 μm thickbut in another embodiment, 4 to 6 μm thick. When it has a thicknesswithin these ranges, it may appropriately maintain heat resistance andthereby, suppress thermal contraction and control metal ion elution.

According to one embodiment of the present invention, since a separatorincludes a hydroxide compound-containing coating layer on the surface ofa polymer substrate, the polymer substrate does not directly contact anactive material layer.

When a polymer substrate used for a separator directly contacts with anactive material layer, the active material works as an oxidizingcatalyst and oxidizes the polymer, eluting a metal ion (particularlysevere at a high temperature). However, a separator according to oneembodiment of the present invention can make an active material layernot in direct contact with a polymer substrate and thus, suppresseselution of metal ions.

In particular, a polymer substrate is severely oxidized through directcontact with an active material layer when a lithium nickel-basedcompound is used as a positive active material. Accordingly, a separatorincluding a hydroxide compound-containing coating layer on the surfaceof a polymer substrate according to one embodiment of the presentinvention may have maximum effects when a lithium nickel-based compoundis used as a positive active material for a rechargeable lithiumbattery.

The lithium nickel-based compounds are compounds comprising both Li andNi and may include compounds represented by the following ChemicalFormulas 1 to 3 or a combination thereof.

Li_(g)Ni_(h)L_(1-j)O_(e)   Chemical Formula 1

In the Chemical Formula 1, 0.8≦g≦2, 0≦h≦1, e is 1 to 2, 0≦j≦1, and

L is Al, Mn, Mg, Zr, or La, or a combination thereof.

Li_(x)Ni_(y)Co_(z)L′_(1-y-z)O_(q)   Chemical Formula 2

In the Chemical Formula 2, 0.65≦x≦1, 0≦y≦1, 0≦z≦1, 0≦y+z≦1, q rangesfrom 1.8 to 2, and

L′ is Al, Mn, Mg, Zr, or La, or a combination thereof.

Li_(x)MO_(2-z)L_(z)   Chemical Formula 3

In the above Chemical Formula 3, M is M′_(1-k)A_(k) (M′ isNi_(1-d-e)Mn_(d)Co_(e), 0.65≦d+e≦0.85, 0.1≦e≦0.4, A is a dopant, forexample B, Ca, Zr, S, F, P, Bi, Al, Mg, Zn, Sr, Cu, Fe, Ga, In, Cr, Ge,or Sn, and 0≦k<0.05),

L is F, S, or P, or a combination thereof,

0.95≦x≦1.05, and

0≦z≦2.

In a rechargeable lithium battery according to one embodiment, thenegative electrode includes a Si-based negative active material, forexample Si, SiO_(x) (0<x<2), a Si-Q alloy, or a combination thereof.Herein, Q is an alkali metal, an alkaline-earth metal, a Group 13element, a Group 14 element, transition elements, or a rare earthelement, or a combination thereof, provided that Q is not Si.

In a rechargeable lithium battery according to one embodiment, anelectrolyte includes a lithium salt and a non-aqueous organic solvent.The non-aqueous organic solvent includes ethylene carbonate-basedorganic solvent by the following Chemical Formula 4. In addition, therechargeable lithium battery according to one embodiment of the presentinvention does not have shortcomings regarding degradation of cycle-lifecharacteristics at high temperatures. Especially, this effect may bemore suitably obtained in the rechargeable lithium battery with aSi-based negative active material, since this battery includes anelectrolyte with an excess ethylene carbonate-based organic solvent inorder to improve cycle-life characteristics at room temperature.

Accordingly, among the non-aqueous organic solvents, an ethylenecarbonate-based organic solvent of the following Chemical Formula 4 maybe used in an amount of 10 to 30 wt % based on the entire weight of anon-aqueous organic solvent, but in another embodiment, in an amount of15 to 25 wt %. When the ethylene carbonate-based organic solvent of thefollowing Chemical Formula 4 is used as a non-aqueous organic solventfor an electrolyte, and especially, when it is used in an amount of 10to 30 wt % based on the entire weight of a non-aqueous organic solvent,room temperature cycle-life characteristic of a rechargeable lithiumbattery including an Si-based negative active material may be improved.

In the above Chemical Formula 4, R₁ and R₂ are the same or different andare hydrogen, a halogen, a cyano (CN), or a nitro (NO₂), or asubstituted alkyl, provided that at least one of R₁ and R₂ is a halogen,or a substituted alkyl. The alkyl may be a C1 to C5 alkyl. Thesubstituted alkyl may be an alkyl in which at least one hydrogen issubstituted with fluorine.

The compounds of the above Chemical Formula 4 include difluoroethylenecarbonate, chloroethylene carbonate, dichloroethylene carbonate,bromoethylene carbonate, dibromoethylene carbonate, nitroethylenecarbonate, cyanoethylene carbonate, or fluoroethylene carbonate, or acombination thereof. According to another embodiment of the presentinvention, a compound represented by the above Chemical Formula 4 may befluoroethylene carbonate.

The non-aqueous organic solvent may include an ethylene carbonate-basedorganic solvent represented by the above Chemical Formula 4 as a firstsolvent and a carbonate-based solvent including no halogen as a secondsolvent. The second solvent may include ester-based, ether-based,ketone-based, alcohol-based, or aprotic solvent, or a combinationthereof along with the carbonate-based solvent. For the second solvent,the carbonate-based solvent includes dimethyl carbonate (DMC), diethylcarbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC),ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), orbutylene carbonate (BC), or a combination thereof.

The ester-based solvent may include methyl acetate, ethyl acetate,n-propyl acetate, dimethylacetate, methylpropinonate, ethylpropinonate,γ-butyrolactone, decanolide, valerolactone, mevalonolactone, orcaprolactone, or a combination thereof. The ether-based solvent mayinclude dibutyl ether, tetraglyme, diglyme, dimethoxyethane,2-methyltetrahydrofuran, or tetrahydrofuran, or a combination thereof.

The ketone-based solvent may include cyclohexanone, and thealcohol-based solvent may include ethanol, isopropyl alcohol, or acombination thereof. The aprotic solvent may include nitriles such asR—CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon,a double bond, an aromatic ring, or an ether bond); amides such asdimethyl formamide, or dimethyl acetamide; dioxolanes such as1,3-dioxolane; sulfolanes; or a combination thereof.

The second solvent may be used singularly or as a mixture. When theorganic solvent is used as a mixture, the mixture ratio can becontrolled in accordance with a desirable battery performance.

When the second solvent is a carbonate-based solvent, a mixture of acyclic carbonate and a linear carbonate may be used. The cycliccarbonate and the linear carbonate are mixed together in a volume ratioof 1:1 to 1:9, and when this mixture is used as an electrolyte, theelectrolyte performance may be enhanced.

For the second solvent, a mixture of carbonate-based solvents andaromatic hydrocarbon-based solvents may be used. The carbonate-basedsolvents and the aromatic hydrocarbon-based solvents are mixed togetherin a volume ratio of 1:1 to 30:1.

The aromatic hydrocarbon-based organic solvent may be represented by thefollowing Chemical Formula 5.

In the above Chemical Formula 5, R₁₁ to R₁₆ are the same or different,and are hydrogen, halogen, a C1 to C10 alkyl, or a C1 to C10 haloalkyl,or a combination thereof.

The aromatic hydrocarbon-based organic solvent may include at least oneof benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene,1,4-difluorobenzene, 1,2,3-triuorobenzene, 1,2,4-trifluorobenzene,chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene,1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene.iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene,1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene,2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene,2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene,2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene,2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene,2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene,2,3,4-triiodotoluene, 2,3,5-triiodotoluene, or xylene, or a combinationthereof.

The electrolyte may include vinylene carbonate to improve batterycycle-life. The amount of the vinylene carbonate is controlled toimprove cycle-life.

The electrolyte may include a nitrile-based additive to improve hightemperature cycle-life characteristics. The nitrile-based additiveincludes succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, orsuberonitrile, or a combination thereof. The nitrile-based additive maybe used in an amount of about 3 to about 5 wt % based on the weight ofthe electrolyte including the non-aqueous organic solvent and a lithiumsalt.

The lithium salt supplies lithium ions in the battery, and so performs abasic operation of a rechargeable lithium battery, and improves lithiumion transport between positive and negative electrodes. Examples of thelithium salt include at least one supporting salt selected from LiPF₆,LiBF₄, LiSbF₆, LiAsF₆, LiN(SO₂C₂F₅)₂, Li(CF₃SO₂)₂N, LiN(SO₃C₂F₅)₂,LiC₄F₉SO₃, LiClO₄, LiAlO₂, LiAlCl₄, LiN(C_(x)F_(2x+1)SO₂,C_(y)F_(2y+1)SO₂, (where x and y are natural numbers), LiCl, LiI, orLiB(C₂O₄)₂ ((lithium bis(oxalato)borate; LiBOB).

The lithium salt may be used in a concentration ranging from about 0.1 Mto about 2.0 M. When the lithium salt is included at the aboveconcentration range, electrolyte performance and lithium ion mobilitymay be enhanced due to optimal electrolyte conductivity and viscosity.

According to one embodiment of the present invention, the positive andnegative electrodes respectively include a current collector and anactive material layer formed thereon and including an active material.

When the active material layer is a positive active material layer, apositive active material may be included in an amount of 90 to 98 wt %based on the entire weight of the active material layer.

The positive active material layer may further include a binder and aconductive material other than the positive active material. Herein, thebinder and the conductive material may be respectively included in anamount of 1 to 5 wt % based on the entire weight of the positive activematerial layer.

The binder plays a role of attaching positive active material particlestogether and also, a positive active material to a current collector.Examples include polyvinylalcohol, carboxylmethylcellulose,hydroxypropylcellulose, diacetylcellulose, polyvinylchloride,carboxylized polyvinylchloride, polyvinylfluoride, an ethyleneoxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, styrene-butadiene rubber, acrylate styrene-butadienerubber, an epoxy resin, nylon, and the like but is not limited thereto.

The conductive material is used to apply conductivity to an electrode.It may include any conductive material unless it may cause a chemicalchange in a battery and can be for example, metal powder such as naturalgraphite, artificial graphite, carbon black, acetylene black,ketjenblack, carbonfiber, copper, nickel, aluminum, silver, and thelike, metal fiber, and the like. In addition, it may include at leastone conductive material such as polyphenylene derivative and the like ora combination of more than one of the above.

The current collector may include Al but is not limited thereto.

The positive active material layer may be formed by coating a positiveactive material composition prepared by mixing a positive activematerial, a binder, a conductive material, and an organic solvent asslurry on a current collector. The solvent may includeN-methylpyrrolidone and the like but is not limited thereto. On theother hand, a method of manufacturing the positive electrode iswell-known in the art and thus is not illustrated in detail.

When the active material layer is a negative active material layer, anegative active material may be included in an amount of 85 to 95 wt %based on the entire weight of the negative active material layer.

The negative active material layer may also include a binder andselectively a conductive material. The binder may be included in anamount of 1 to 5 wt % based on the entire amount of a negative activematerial. In addition, when the negative active material layer includesa conductive material, it may include a negative active material in anamount of 85 to 95 wt %, a binder in an amount of 5 to 15 wt %, and aconductive material in an amount of 0 to 5 wt %.

The binder plays a role of attaching negative active material particlesto one another and a negative active material to a current collector.The binder may include a non-water-soluble binder, a water-solublebinder, or a combination thereof.

The non-water-soluble binder may include polyvinylchloride, carboxylatedpolyvinylchloride, polyvinylfluoride, an ethylene oxide-containingpolymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene,polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, orpolyimide, or a combination thereof.

The water-soluble binder may include styrene-butadiene rubber, acrylatedstyrene-butadiene rubber, polyvinylalcohol, sodium polyacrylate, anolefin copolymer with propylene and 2 to 8 carbons, or a copolymer of(metha)acrylic acid and (metha)acrylic acid and alkylester, or acombination thereof.

When the negative electrode binder is a water-soluble binder, it mayfurther include a cellulose-based compound being able to enhanceviscosity. The cellulose-based compound may include carboxylmethylcellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkalimetal salt thereof, or a combination thereof. The alkali metal mayinclude Na, K, or Li. It may be used in an amount of 0.1 to 3 parts byweight based on 100 parts by weight of a binder.

The conductive material is used to supply conductivity to an electrode.However, it may include any conductive material unless it may cause anychemical change. Examples of the conductive material may include acarbon-based material such as natural graphite, artificial graphite,carbon black, acetylene black, ketjen black, carbon fiber, and the like;a metal-based material such as metal powder such as copper, nickel,aluminum, silver, and the like, metal fiber, or the like; and aconductive material such as a conductive polymer such as polyphenylenederivative and the like or a mixture thereof.

The current collector may include a copper film, a nickel film, astainless steel film, a titanium film, a nickel foam, a copper foam, ora polymer substrate coated with a conductive material, or a combinationthereof.

The negative electrode is prepared by preparing a negative activematerial composition prepared by mixing a negative active material, abinder and selectively a conductive material in a solvent and coatingthe composition on a current collector. This method of manufacturing anelectrode is well-known in the art and is not illustrated in detail.When the solvent includes a non-water-soluble binder, it may be anorganic solvent such as N-methylpyrrolidone and the like. When itincludes a water-soluble binder, it may be water but is not limitedthereto.

FIG. 1 shows the structure of a rechargeable lithium battery accordingto one embodiment of the present invention. However, the rechargeablelithium battery of the present invention is not limited to the structureshown in FIG. 1, but includes any shape such as cylinder, prism, coin,pouch, and the like. As shown in FIG. 1, the rechargeable lithiumbattery 1 may include a negative electrode 2, a positive electrode 3,and a separator 4 disposed between the negative electrode 2 and positiveelectrode 3, an electrolyte (not shown) impregnated between the negativeelectrode 2, the positive electrode 3, and the separator 4, a batterycase 5, and a sealing member 6 sealing the battery case 5.

The following examples illustrate this disclosure in more detail. Thefollowing examples are not more than specific examples of thisdisclosure, and the scope of this disclosure is not limited by theExamples.

EXAMPLE 1

94 wt % of a mixed positive active material ofLiNi_(0.8)Co_(0.15)Al_(0.05)O₂ and Li₂NiO₂ in a ratio of 90 wt %: 10 wt%, 3 wt % of a carbon black conductive material, and 3 wt % of apolyvinylidene fluoride binder were mixed in N-methylpyrrolidone toprepare a positive active material slurry. This slurry was coated on analuminum foil current collector and then, dried and compressed,preparing a positive electrode.

92 wt % of a SiO_(x) (x=0.99) negative active material and 8 wt % of apolyamideimide binder were mixed in N-methylpyrrolidone, preparingnegative active material slurry. This slurry was coated on a copper foilcurrent collector and then, dried and compressed, preparing a negativeelectrode.

Next, a mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 10 volume %:20 volume %:20 volume %:50 volume % ratio, and 1.3Mof LiPF₆ was added thereto. Then, succinonitrile was added to thismixture in an amount of 5 wt % based on the entire weight of themixture, preparing an electrolyte.

Al(OH)₃ and a meta-aramid resin was mixed in a ratio of 80:20 wt % in anN-methylpyrrolidone solvent to prepare a coating layer composition. Thecoating layer composition was coated on both sides of a 10 μm-thickpolyethylene substrate to prepare a separator. The coating layerincluding Al(OH)₃ and an aramid resin was formed to be 5 μm thick.

The positive electrode, the negative electrode, the electrolyte, and theseparator were used to fabricate a lithium fuel cell.

EXAMPLE 2

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 20 volume %:10 volume %:20 volume %:50 volume %, and 1.0M ofLiPF₆ was added thereto. Next, succinonitrile was added to this mixturein an amount of 5 wt % based on the entire weight of the mixture,preparing an electrolyte. Then, a lithium fuel cell was fabricatedaccording to the same method as Example 1 except for the electrolyte.

EXAMPLE 3

Fluoroethylene carbonate, ethylmethyl carbonate, and diethylcarbonatewere mixed in a ratio of 30 volume %:20 volume %:50 volume % to preparea mixed solvent, and 1.0M LiPF₆ was added thereto. Succinonitrile wasadded to the resulting mixture in an amount of 5 wt % based on theentire weight of the mixture, preparing an electrolyte. Then, a lithiumfuel cell was fabricated according to the same method as Example 1except for the electrolyte.

EXAMPLE 4

A mixed solvent was prepared by mixing ethylene carbonate, ethylmethylcarbonate, and diethylcarbonate in a weight ratio of 30 volume %:20volume %:50 volume %, and 1.3M of LiPF₆ was added thereto. Next,succinonitrile was added to the resulting mixture in an amount of 5 wt %based on the entire weight of the mixture, preparing an electrolyte.Then, a lithium fuel cell was fabricated according to the same method asExample 1 except for the electrolyte.

EXAMPLE 5

Mg(OH)₂ and a meta-aramid resin were mixed in a ratio of 80:20 wt % inan N-methylpyrrolidone solvent to prepare a coating layer composition.This coating layer composition was coated to be 5 μm thick on both sidesof a 10 μm-thick polyethylene substrate, fabricating a separator. Thecoating layer included Mg(OH)₂ and an aramid resin.

94 wt % of a mixed positive active material prepared by mixingLiNi_(0.8)Co_(0.15)Al_(0.05)O₂ and Li₂NiO₂ in a ratio of 90 wt %:10 wt%, 3 wt % of a carbon black conductive material, and 3 wt % of apolyvinylidene fluoride binder were mixed in N-methylpyrrolidone toprepare a positive active material slurry. This slurry was coated on analuminum foil current collector and then, dried and compressed,fabricating a positive electrode.

92 wt % of a SiO_(x) (x=0.99) negative active material and 5 wt % of apolyamideimide binder were mixed in N-methylpyrrolidone, preparing anegative active material slurry. This slurry was coated on a copper foilcurrent collector and then, dried and compressed, fabricating a negativeelectrode.

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 10 volume %:20 volume %:20 volume %:50 volume %, and 1.3M LiPF₆was added thereto. Next, succinonitrile was added to the resultingmixture in an amount of 5 wt % based on the entire weight of themixture, preparing an electrolyte.

The separator, the positive electrode, the negative electrode, and theelectrolyte were used to fabricate a lithium fuel cell.

EXAMPLE 6

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 20 volume %:10 volume %:20 volume %:50 volume %, and 1.0M ofLiPF₆ was added thereto. Next, succinonitrile was added to the resultingmixture in an amount of 5 wt % based on the entire weight of themixture, preparing an electrolyte. Then, a lithium fuel cell wasfabricated according to the same method as Example 5 except for theelectrolyte.

EXAMPLE 7

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylmethyl carbonate, and diethylcarbonate in a ratio of 30 volume %:20volume %:50 volume %, and LOM of LiPF₆ was added to thereto. Next,succinonitrile was added to the resulting mixture in an amount of 5 wt %based on the entire weight of the mixture, preparing an electrolyte.Then, a lithium fuel cell was fabricated according to the same method asExample 5 except for the electrolyte.

EXAMPLE 8

A mixed solvent was prepared by mixing ethylene carbonate, ethylmethylcarbonate, and diethylcarbonate in a ratio of 30 volume %:20 volume %:50volume %, and 1.3M of LiPF₆ was added thereto. Next, succinonitrile wasadded to the resulting mixture in an amount of 5 wt % based on theentire weight of the mixture, preparing an electrolyte. Then, a lithiumfuel cell was fabricated according to the same method as Example 5except for the electrolyte.

COMPARATIVE EXAMPLE 1

94 wt % of a positive active material prepared by mixingLiNi_(0.8)Co_(0.15)Al_(0.05)O₂ and Li₂NiO₂ in a ratio of 90 wt %:10 wt%, 3 wt % of a carbon black conductive material, and 3 wt % of apolyvinylidene fluoride binder were mixed in N-methylpyrrolidone,preparing positive active material slurry. This slurry was coated on analuminum foil current collector and then, dried and compressed,fabricating a positive electrode.

92 wt % of a SiO_(x) (x=0.99) negative active material and 8 wt % of apolyamideimide binder were mixed in N-methylpyrrolidone to prepare anegative active material slurry. This slurry was coated on a copper foilcurrent collector and then, dried and compressed, fabricating a negativeelectrode.

In addition, fluoroethylene carbonate, ethylene carbonate, ethylmethylcarbonate, and diethylcarbonate were mixed in a ratio of 10 volume %:20volume %:20 volume %:50 volume % to prepare a mixed solvent, and 1.3M ofLiPF₆ was added thereto. Next, succinonitrile was added to the resultingmixture in an amount of 5 wt % based on the entire weight of themixture, preparing an electrolyte.

As for a separator, used was a 20 μm-thick polyethylene film. Thepositive electrode, the negative electrode, the electrolyte, and theseparator were used to fabricate a lithium fuel cell.

COMPARATIVE EXAMPLE 2

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 20 volume %:10 volume %:20 volume %:50 volume %, and 1.0M ofLiPF₆ was added thereto. Next, succinonitrile was added to the mixturein an amount of 5 wt % based on the entire weight of the mixture,preparing an electrolyte. Then, a lithium fuel cell was fabricatedaccording to the same method as Comparative Example 1 except for theelectrolyte.

COMPARATIVE EXAMPLE 3

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylmethyl carbonate, and diethylcarbonate in a ratio of 30 volume %:20volume %:50 volume %, and 1.0M of LiPF₆ was added thereto. Next,succinonitrile was added to the resulting mixture in an amount of 5 wt %based on the entire weight of the mixture, preparing an electrolyte.Then, a lithium fuel cell was fabricated according to the same method asComparative Example 1 except for the electrolyte.

COMPARATIVE EXAMPLE 4

A mixed solvent was prepared by mixing ethylene carbonate, ethylmethylcarbonate, and diethylcarbonate in a ratio of 30 volume %:20 volume %:50volume %, and 1.3M of LiPF₆ was added thereto. Next, succinonitrile wasadded to the resulting mixture in an amount of 5 wt % based on theentire weight of the mixture, preparing an electrolyte. Then, a lithiumfuel cell was fabricated according to the same method as ComparativeExample 1 except for the electrolyte.

COMPARATIVE EXAMPLE 5

Positive active material slurry was prepared by mixing 94 wt % of aLiCoO₂ positive active material, 3 wt % of a carbon black conductivematerial, and 3 wt % of a polyvinylidene fluoride binder inN-methylpyrrolidone. The slurry was coated on an aluminum foil currentcollector and then, dried and compressed, fabricating a positiveelectrode.

92 wt % of a SiO_(x) (x=0.99) negative active material and 8 wt % of apolyamideimide binder were mixed in N-methylpyrrolidone to prepare anegative active material slurry. This slurry was coated on a copper foilcurrent collector and then, dried and compressed, fabricating a negativeelectrode.

In addition, a mixed solvent was prepared by mixing fluoroethylenecarbonate, ethylene carbonate, ethylmethyl carbonate, anddiethylcarbonate in a ratio of 10 volume %:20 volume %:20 volume %:50volume %, and 1.3M of LiPF₆ was added thereto. Next, succinonitrile wasadded to the resulting mixture in an amount of 5 wt % based on theentire weight of the mixture, preparing an electrolyte.

Then, the positive electrode, the negative electrode, the electrolyte,and a 20 μm-thick polyethylene film separator were used to fabricate alithium fuel cell.

COMPARATIVE EXAMPLE 6

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 20 volume %:10 volume %:20 volume %:50 volume %, and 1.0M of LiPF₆ was added thereto. Next, succinonitrile was added to the mixture inan amount of 5 wt % based on the entire weight of the mixture, preparingan electrolyte. Then, a lithium fuel cell was fabricated according tothe same method as Comparative Example 5 except for the electrolyte.

COMPARATIVE EXAMPLE 7

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 30 volume %:20 volume %:50 volume %, and 1.0M of LiPF₆ wasadded thereto. Next, succinonitrile was added to the mixture in anamount of 5 wt % based on the entire weight of the mixture, preparing anelectrolyte. Then, a lithium fuel cell was fabricated according to thesame method as Comparative Example 5 except for the electrolyte.

COMPARATIVE EXAMPLE 8

A mixed solvent was prepared by mixing ethylene carbonate, ethylenecarbonate, ethylmethyl carbonate, and diethylcarbonate in a ratio of 30volume %:20 volume %:50 volume %, and 1.3M of LiPF₆ was added thereto.Next, succinonitrile was added to the mixture in an amount of 5 wt %based on the entire weight of the mixture, preparing an electrolyte.Then, a lithium fuel cell was fabricated according to the same method asComparative Example 5 except for the electrolyte.

COMPARATIVE EXAMPLE 9

Positive active material slurry was prepared by mixing 94 wt % of aLiCoO₂ positive active material, 3 wt % of a carbon black conductivematerial, and 3 wt % of a polyvinylidene fluoride binder inN-methylpyrrolidone. The slurry was coated on an aluminum foil currentcollector and then, dried and compressed, fabricating a positiveelectrode.

92 wt % of a SiO_(x) (x=0.99) negative active material and 8 wt % of apolyamideimide binder were mixed in N-methylpyrrolidone to prepare anegative active material slurry.

This slurry was coated on a copper foil current collector and then,dried and compressed, fabricating a negative electrode.

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 10 volume %:20 volume %:20 volume %:50 volume %, and 1.3M ofLiPF₆ was added thereto. Next, succinonitrile was added to the mixturein an amount of 5 wt % based on the entire weight of the mixture,preparing an electrolyte.

Then, a separator was prepared by preparing a coating layer compositionby mixing Al(OH)₃ and a meta-aramid resin in a ratio of 80:20 wt % in anN-methylpyrrolidone solvent and coating the coating layer composition onboth sides of a 10 μm-thick polyethylene substrate to form a 5 μm-thickcoating layer including Al(OH)₃ and an aramid resin.

The positive electrode, the negative electrode, the electrolyte, and theseparator were used to fabricate a lithium fuel cell.

COMPARATIVE EXAMPLE 10

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 20 volume %:10 volume %:20 volume %:50 volume %, and 1.0M ofLiPF₆ was added thereto. Next, succinonitrile was added to the mixturein an amount of 5 wt % based on the entire weight of the mixture,preparing an electrolyte. Then, a lithium fuel cell was fabricatedaccording to the same method as Comparative Example 9 except for theelectrolyte.

COMPARATIVE EXAMPLE 11

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylmethyl carbonate, and diethylcarbonate in a ratio of 30 volume %:20volume %:50 volume %, and 1.0M of LiPF₆ was added thereto. Next,succinonitrile was added to the mixture in an amount of 5 wt % based onthe entire weight of the mixture, preparing an electrolyte. Then, alithium fuel cell was fabricated according to the same method asComparative Example 9 except for the electrolyte.

COMPARATIVE EXAMPLE 12

A mixed solvent was prepared by mixing ethylene carbonate, ethylmethylcarbonate, and diethylcarbonate in a ratio of 30 volume %:20 volume %:50volume %, and 1.3M of LiPF₆ was added thereto. Next, succinonitrile wasadded to the mixture in an amount of 5 wt % based on the entire weightof the mixture, preparing an electrolyte. Then, a lithium fuel cell wasfabricated according to the same method as Comparative Example 9 exceptfor the electrolyte.

COMPARATIVE EXAMPLE 13

A separator was prepared by preparing a coating layer composition bymixing Mg(OH)₂ and a meta-aramid resin in a ratio of 80:20 wt % in anN-methylpyrrolidone solvent and coating the coating layer composition onboth sides of a 10 μm-thick polyethylene substrate to form a 5 μm-thickcoating layer including Mg(OH)₂ and an aramid resin.

Positive active material slurry was prepared by mixing 94 wt % of aLiCoO₂ positive active material, 3 wt % of a carbon black conductivematerial, and 3 wt % of a polyvinylidene fluoride binder inN-methylpyrrolidone. The slurry was coated on an aluminum foil currentcollector and then, dried and compressed, fabricating a positiveelectrode.

A negative active material slurry was prepared by mixing 92 wt % of aSiO_(x) (x=0.99) negative active material and 8 wt % of a polyamideimidebinder in N-methylpyrrolidone. This slurry was coated on a copper foilcurrent collector and then, dried and compressed, fabricating a negativeelectrode.

Then, a mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 10 volume %:20 volume %:20 volume %:50 volume %, and 1.3M ofLiPF₆ was added thereto. Next, succinonitrile was added to the mixturein an amount of 5 wt % based on the entire weight of the mixture,preparing an electrolyte.

The separator, the positive electrode, the negative electrode, and theelectrolyte were used to fabricate a lithium fuel cell.

COMPARATIVE EXAMPLE 14

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylene carbonate, ethylmethyl carbonate, and diethylcarbonate in aratio of 20 volume %:10 volume %:20 volume %:50 volume %, and 1.0M ofLiPF₆ was added thereto. Next, succinonitrile was added to the mixturein an amount of 5 wt % based on the entire weight of the mixture,preparing an electrolyte. Then, a lithium fuel cell was fabricatedaccording to the same method as Comparative Example 13 except for theelectrolyte.

COMPARATIVE EXAMPLE 15

A mixed solvent was prepared by mixing fluoroethylene carbonate,ethylmethyl carbonate, and diethylcarbonate in a ratio of 30 volume %:20volume %:50 volume %, and 1.0M of LiPF₆ was added thereto. Next,succinonitrile was added to the mixture in an amount of 5 wt % based onthe entire weight of the mixture, preparing an electrolyte. Then, alithium fuel cell was fabricated according to the same method asComparative Example 1 except for the electrolyte.

COMPARATIVE EXAMPLE 16

A mixed solvent was prepared by mixing ethylene carbonate, ethylmethylcarbonate, and diethylcarbonate in a ratio of 30 volume %:20 volume %:50volume %, and 1.3M of LiPF₆ was added thereto. Next, succinonitrile wasadded to the mixture in an amount of 5 wt % based on the entire weightof the mixture, preparing an electrolyte. Then, a lithium fuel cell wasfabricated according to the same method as Comparative Example 13 exceptfor the electrolyte.

The lithium fuel cells according to Examples 1 to 4 and ComparativeExamples 1 to 4 were 100 times charged with 0.8 C and discharged with 1C at room temperature of 25° C. Then, a ratio of 100^(th) dischargecapacity against 1^(st) discharge capacity was calculated for cycle-lifecharacteristic at room temperature. The results are provided in thefollowing Table 1.

The lithium fuel cells according to Examples 1 to 4 and ComparativeExamples 1 to 4 were 100 times charged with 0.8 C and discharged with 1C at a high temperature of 45° C. Likewise, a ratio of 100^(th)discharge capacity against 1^(st) discharge capacity was calculated forcycle-life characteristic at a high temperature. The results areprovided in the following Table 1.

TABLE 1 positive active material: positive active material: positiveactive material: NCA + LNO NCA + LNO NCA + LNO negative active material:SiO_(x) negative active material: SiO_(x) negative active material:SiO_(x) electrolyte without separator coating layer separator coatinglayer: Al (OH)₃ separator coating layer: Mg (OH)₂ solution r.t. cycle-h.t. cycle- r.t. cycle- h.t. cycle- r.t. cycle- h.t cycle- compositionlife (%) life (%) life (%) life (%) life (%) life (%) FEC 0 Comp. 85 53Ex. 4 86 80 Ex. 8 85 78 volume % Ex. 4 FEC 10 Comp. 87 51 Ex. 1 87 79Ex. 5 88 79 volume % Ex. 1 FEC 20 Comp. 92 47 Ex. 2 91 81 Ex. 6 90 79volume % Ex. 2 FEC 30 Comp. 92 48 Ex. 3 91 80 Ex. 7 91 81 volume % Ex. 3

In Table 1, NCA+LNO indicate a positive active material prepared bymixing LiNi_(0.8)Co_(0.15)Al_(0.05)O₂ and Li₂NiO₂. FEC indicatesfluoroethylene carbonate.

Furthermore, in Table 1, r.t. indicates room temperature, and h.t.indicates high temperature. In Table 1, Comp. Ex. indicates comparativeexample, and Ex. indicates example.

As shown in Table 1, the lithium fuel cells including a separatorprepared by coating Al(OH)₃ on a polyethylene substrate according toExamples 1 to 4 and by coating on Mg(OH)₂ a polyethylene substrateaccording to Examples 5 to 8 had almost similar cycle-lifecharacteristic at room and high temperatures. In other words, thelithium fuel cells according to Examples 1 to 8 had almost no cycle-lifecharacteristic degradation at a high temperature. On the contrary, theones of Comparative Examples 1 to 4 had abruptly deteriorated cycle-lifecharacteristic at a high temperature.

In addition, the lithium fuel cells according to Comparative Example 5to 16 were 100 times charged with 0.8 C and discharged with 1 C at roomtemperature of 25° C. Then, a ratio of 100th discharge capacity against1st discharge capacity was calculated for cycle-life characteristic atroom temperature. The result is provided in the following Table 2. Theywere also 100 times charged with 0.8 C and discharged with 1 C at a hightemperature of 45° C. Then, a ratio of 100th discharge capacity against1st discharge capacity was calculated for cycle-life characteristic at ahigh temperature. The results are provided in the following Table 2.

TABLE 2 positive active material: LCO positive active material: LCOpositive active material: LCO negative active material: SiO_(x) negativeactive material: SiO_(x) negative active material: SiO_(x) electrolytewithout separator coating layer separator coating layer: Al (OH)₃separator coating layer: Mg (OH)₂ solution r.t. cycle- h.t. cycle- r.t.cycle- h.t. cycle- r.t. cycle- h.t. cycle- composition life (%) life (%)life (%) life (%) life (%) life (%) FEC 0 Comp. 68 71 Comp. 70 75 Comp.71 76 volume % Ex. 8 Ex. 12 Ex. 16 FEC 10 Comp. 74 77 Comp. 75 79 Comp.74 78 volume % Ex. 5 Ex. 9 Ex. 13 FEC 20 Comp. 81 78 Comp. 82 85 Comp.83 84 volume % Ex. 6 Ex. 10 Ex. 14 FEC 30 Comp. 85 82 Comp. 87 90 Comp.86 88 volume % Ex. 7 Ex. 11 Ex. 15

In the Table 2, LCO indicates LiCoO₂.

Furthermore, in Table 2, r.t. indicates room temperature, and h.t.indicates high temperature. In Table 2, Comp. Ex. indicates comparativeexample, and Ex. indicates example.

As shown in Table 2, when LiCoO₂ was used as a positive active material,the lithium fuel cells had almost no high temperature cycle-lifedegradation. Accordingly, when used was a polyethylene film separatorcoated with Al(OH)₃ or Mg(OH)₂, the lithium fuel cells had littlecycle-life characteristic improvement at high temperature.

As shown in Tables 1 and 2, when a lithium nickel-based positive activematerial, an SiO_(x) negative active material, and a polyethylene filmseparator coated with Al(OH)₃ or Mg(OH)₂ and FEC was used, the lithiumfuel cells had improved cycle-life characteristic at room and hightemperatures.

In addition, when a cobalt-based positive active material and an SiOxnegative active material were used, there was no additional effect dueto polyethylene film separator coated with Al(OH)₃ or Mg(OH)₂.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. Therefore, the aforementioned embodimentsare exemplary in every way but not limited.

1. A separator for a rechargeable lithium battery, comprising: a polymersubstrate; and a coating layer comprising a hydroxide compound disposedon the polymer substrate.
 2. The separator of claim 1, wherein thehydroxide compound comprises Al(OH)₃, Mg(OH)₂, Ti(OH)₄, or Si(OH)₄, or acombination thereof.
 3. The separator of claim 1, wherein the coatinglayer further comprises a heat-resistant resin.
 4. The separator ofclaim 1, wherein the coating layer further comprises a heat-resistantresin including an aramid resin, a polyamideimide resin, or a polyimideresin, or a combination thereof.
 5. The separator of claim 1, whereinthe coating layer further comprises a heat-resistant resin, and themixing ratio of the hydroxide compound and the heat-resistant resin is50:50 to 90:10 wt %.
 6. The separator of claim 1, wherein the polymersubstrate is a substrate including a polyolefin resin.
 7. The separatorof claim 1, wherein the coating layer is disposed on one side of thepolymer substrate or both sides of the polymer substrate.
 8. Theseparator of claim 1, wherein the polymer substrate has a thickness of 8μm to 20 μm.
 9. The separator of claim 1, wherein the coating layer hasa thickness of 2 μm to 8 μm.